Sounding mechanism and configuration under carrier aggregation

ABSTRACT

A method of multi-set RRC signaling for ap-SRS configuration is provided to enhance ap-SRS flexibility. An eNB transmits a plurality of sets of UE-specific SRS parameters to a UE via upper layer messaging in a multi-carrier wireless communication system. The eNB also determines triggering information of a selected set of UE-specific SRS parameters and an indicated carrier for the UE. The eNB then transmits an uplink or downlink grant over a primary carrier, the grant comprises triggering information for the UE to send an ap-SRS over the indicated carrier using the selected set of UE-specific SRS parameters. In one embodiment of joint signaling, the plurality of sets of UE-specific SRS parameters are signaled together in a single RRC transmission. In another embodiment of separate signaling, each set of UE-specific SRS parameters is signaled independently.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation, and claims priority under 35 U.S.C.§120 from nonprovisional U.S. patent application Ser. No. 13/373,071,entitled “Sounding Mechanism and Configuration under CarrierAggregation,” filed on Nov. 1, 2011, the subject matter of which isincorporated herein by reference. Application Ser. No. 13/373,071, inturn, is a continuation-in-part of, and claims priority under 35 U.S.C.§120 from nonprovisional U.S. patent application Ser. No. 13/134,811,entitled “Sounding Mechanism under Carrier Aggregation,” filed on Jun.17, 2011, the subject matter of which is incorporated herein byreference. Application Ser. No. 13/134,811, in turn, claims priorityunder 35 U.S.C. §119 from U.S. Provisional Application No. 61/356,077,entitled “Sounding Operation under Carrier Aggregation Scenarios,” filedon Jun. 18, 2010, the subject matter of which is incorporated herein byreference. This application also claims priority under 35 U.S.C. §119from U.S. Provisional Application No. 61/409,733, entitled “Method ofCell Configuration and Management,” filed on Nov. 3, 2010, the subjectmatter of which is incorporated by reference.

TECHNICAL FIELD

The disclosed embodiments relate generally to wireless networkcommunications, and, more particularly, to sounding channel signaling inLTE-A systems under carrier aggregation.

BACKGROUND

Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-userversion of the Orthogonal Frequency-Division Multiplexing (OFDM) digitalmodulation technology. In wireless OFDMA systems, however, multipath isan undesirable propagation phenomenon that results in radio signalsreaching the receiving antenna by two or more paths. Signal variationsin amplitude or phase resulted from multipath are also referred aschannel response. Transmission techniques, in which a transmitter makesuse of the channel response between the transmitter and a receiver, arecalled close-loop transmission techniques. In multiple-inputmultiple-output (MIMO) applications, close-loop transmission techniquesare much more robust as compared with open-loop MIMO techniques.

One method of providing channel information to the transmitter is viathe use of an uplink (UL) sounding channel. Channel sounding is asignaling mechanism where a mobile station (also referred to as a userequipment (UE)) transmits sounding reference signals (SRS) on an uplinkchannel to enable a base station (also referred to as an eNodeB) toestimate the UL channel response. Channel sounding assumes thereciprocity of uplink and downlink channels, which is generally true inTime Division Duplexing (TDD) systems. Because the frequency bandwidthof the UL transmission encompasses the frequency bandwidth of the DLtransmission in TDD systems, UL channel sounding can enable close-loopSU/MU-MIMO in downlink transmission. For example, the eNodeB can performnon-codebook based downlink beamforming based on channel stateinformation (CSI) measured via SRS. UL channel sounding can also enableUL close-loop MIMO transmission in both TDD and Frequency DivisionDuplexing (FDD) systems. For example, the eNodeB can perform codebookbased uplink beamforming by choosing the best precoding weights(vectors/matrices) (e.g., select the best PMI from the codebook) to beused for the UE based on CSI measured by SRS, such that the UE canperform close-loop SU/MU-MIMO in UL transmission. In TDD system, ULchannel sounding can also be used for frequency selective scheduling,where the eNodeB schedules the UE to its best frequency band in bothdownlink and uplink transmissions.

In 3GPP LTE-Advanced (LTE-A) wireless communication systems, two typesof SRS are defined. A first type of Periodic SRS (p-SRS) is used forobtaining long-term channel information. The periodicity of p-SRS is ingeneral long (up to 320 ms) to reduce overhead. The p-SRS parameters areconfigured by higher layer radio resource control (RRC), soconfiguration time is long (e.g., 15-20 ms) and signaling flexibility islow. For uplink MIMO supported in Release 10, p-SRS resource is highlydemanded for close-loop spatial multiplexing, especially when the numberof UEs becomes large. A second type of Aperiodic SRS (ap-SRS) is a newfeature introduced in Release 10. Ap-SRS is triggered either by downlinkor uplink grant via physical downlink control channel (PDCCH). Oncetriggered, the UE transmits a sounding sequence in a pre-definedlocation for one-time transmission. Ap-SRS supports multi-antennasounding for uplink MIMO. Ap-SRS is much more flexible than p-SRS.Ap-SRS can use residual resource that is not used by p-SRS bymultiplexing between ap-SRS and p-SRS.

Carrier aggregation (CA) is introduced as part of the overall 4Genhancement in 3GPP LTE-A systems. With carrier aggregation, an LTE-Asystem can support peak target data rates in excess of 1 Gbps in thedownlink (DL) and 500 Mbps in the uplink (UL). Such technology isattractive because it allows operators to aggregate several smallercontiguous or non-continuous component carriers (CC) to provide a largeraggregated system bandwidth, and provides backward compatibility byallowing legacy users to access the system by using one of the componentcarriers. Under carrier aggregation, each UE has one primary carrier(i.e., Pcell) and multiple secondary carriers (i.e., Scell). Incross-carrier scheduling scenario, PDCCH is received via Pcell only.Channel sounding, however, shall be configured in both Pcell and Scell.How to apply PDCCH in Pcell to trigger ap-SRS in Scell is a problemfaced in LTE-A sounding under carrier aggregation.

SUMMARY

Sounding mechanism for LTE-A systems under carrier aggregation isprovided. A user equipment (UE) receives an uplink or downlink granttransmitted from a base station (eNB) over a primary carrier in amulti-carrier LTE-A system. The UE determines indicated carrier(s) anddetects a triggering condition for aperiodic sounding transmission inthe uplink or downlink grant. The uplink or downlink grant istransmitted via a Physical Downlink Control Channel (PDCCH). The UE thenselects UE-specific sounding reference signal (SRS) parameters if thetriggering condition is true. The UE-specific SRS parameters areconfigured via upper layer radio resource control (RRC) signaling.Finally, the UE transmits an aperiodic SRS (ap-SRS) over the indicatedcarrier(s) using the selected UE-specific SRS parameters.

In one embodiment, the uplink grant is transmitted via a PDCCH carryingDCI format 0 or 4, and downlink grant is transmitted via a PDCCHcarrying DCI format 1A, 2B, or 2C. Each DCI format contains a carrierindicator field (CIF) if cross-carrier scheduling is enabled. The CIF isused for scheduling PUSCH transmission or PDSCH reception. In one novelaspect, ap-SRS is transmitted on the carrier indicated by the CIF toachieve cross-carrier scheduling.

In another embodiment, DCI format3/3A is transmitted via a PDCCH to agroup of UEs. DCI format 3/3A contains a plurality of informationfields, each field also can be used to indicate if a UE should enableap-SRS in a particular carrier. The location of each information fieldcorresponds to an indicated carrier of the UE, while the value of eachinformation field corresponds to a triggering condition. Once triggered,the UE transmits an ap-SRS over the indicated one or more carriers.Multiple carriers may be indicated in the same PDCCH.

In one advantageous aspect, multi-set RRC signaling for ap-SRSconfiguration is provided to enhance ap-SRS flexibility. An eNBtransmits a plurality of sets of UE-specific SRS parameters to a UE viaupper layer messaging in a multi-carrier wireless communication system.The eNB also determines triggering information of a selected set ofUE-specific SRS parameters and an indicated carrier for the UE. The eNBthen transmits an uplink or downlink grant over a primary carrier, thegrant comprises triggering information for the UE to send an ap-SRS overthe indicated carrier using the selected set of UE-specific SRSparameters. In one embodiment of joint signaling, the plurality of setsof UE-specific SRS parameters are signaled together in a single RRCtransmission. In another embodiment of separate signaling, each set ofUE-specific SRS parameters is signaled independently. Joint signaling issimple at the cost of large signaling overhead, while separate signalingis more flexible but needs to indicate which set is reconfigured.

Other embodiments and advantages are described in the detaileddescription below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 illustrates uplink channel sounding in multi-carrier wirelesscommunication systems in accordance with one novel aspect.

FIG. 2 illustrates a multi-carrier LTE-A wireless communication systemwith uplink channel sounding in accordance with one novel aspect.

FIG. 3 is a flow chart of a first method of uplink ap-SRS transmissionin accordance with one novel aspect.

FIG. 4 illustrates one embodiment of the first method of uplink ap-SRStriggering mechanism.

FIG. 5 illustrates a detailed example of the first method of uplinkap-SRS transmission.

FIG. 6 is a flow chart of a second method of uplink ap-SRS transmissionin accordance with one novel aspect.

FIG. 7 illustrates one embodiment of the second method of uplink ap-SRStriggering mechanism.

FIG. 8 illustrates one embodiment of multi-set RRC signaling for ap-SRSin accordance with one novel aspect.

FIGS. 9 and 10 are flow charts of a method of multi-set RRC signalingfor ap-SRS configuration.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates uplink channel sounding in a multi-carrier 3GPP LTE-Awireless communication system 10 in accordance with one novel aspect. InLTE wireless communication systems, a base station (also referred to asan eNB, e.g., eNB11) and a mobile station (also referred to as a userequipment (UE), e.g., UE12) communicate with each other by sending andreceiving data carried in a series of frames. Each frame comprises anumber of downlink (DL) subframes for the eNB to transmit data to theUE, and a number of uplink (UL) subframes for the UE to transmit data tothe eNB. Uplink channel sounding is a signaling mechanism to facilitatevarious close-loop transmission techniques such as DL/UL beamforming andfrequency selective scheduling. For uplink channel sounding, the eNBconfigures sounding reference signal (SRS) parameters and allocates SRSresource in a previous DL subframe (e.g., subframe DL13), and the UEtransmits a sounding signal in a subsequent UL subframe (e.g., DL14) toenable the eNB to estimate UL channel response.

In 3GPP LTE-A systems, two types of SRS are defined for uplink channelsounding. A first type of Periodic SRS (p-SRS) is used for obtaininglong-term channel response information. The periodicity of p-SRS is ingeneral long (up to 320 ms). The p-SRS parameters are configured andtriggered by higher layer radio resource control (RRC), so configurationtime is long (e.g., 15-20 ms delay) and signaling flexibility is low. Asecond type of Aperiodic SRS (ap-SRS) is also configured via RRC.Ap-SRS, however, is dynamically triggered by an uplink or downlink grantfrom the eNB. Once triggered, the UE transmits a sounding signal to theeNB in a pre-defined location. Ap-SRS is a new feature introduced inRelease 10 that supports multi-antenna sounding for uplink MIMO. Ap-SRSis much more flexible than p-SRS and can use residual resource that isnot used by p-SRS by multiplexing between ap-SRS and p-SRS.

Traditionally, p-SRS parameters are configured via RRC. To dynamicallytrigger and configure ap-SRS parameters, however, the use of higherlayer RRC is no longer efficient because of the long latency. Therefore,a faster physical layer signaling method is desirable for triggeringap-SRS and configuring ap-SRS parameters. In one example, ap-SRS may betriggered via a physical downlink control channel (PDCCH) that providesreasonable flexibility. In multi-carrier LTE-A systems with carrieraggregation, each UE has one primary carrier (i.e., Pcell) and multiplesecondary carriers (i.e., Scell). In cross-carrier scheduling scenario,PDCCH is received via Pcell only. Uplink channel sounding, however,shall be configured in both Pcell and Scell.

In one novel aspect, an example of uplink channel sounding using ap-SRSwith cross-carrier scheduling is illustrated in FIG. 1. Base stationeNB11 transmits ap-SRS triggering information in an uplink grant over aprimary carrier (e.g., PCELL) in a previous downlink subframe DL13.Based on the ap-SRS triggering information, UE12 detects a triggeringcondition and carrier indication information in the uplink grant. If thetriggering condition is true, then the UE selects the latest RRCconfigured UE-specific ap-SRS parameters, indicated by PDCCH. Finally,UE12 transmits an ap-SRS over an indicated carrier (e.g., SCELL) in asubsequent uplink subframe UL14 by following the selected UE-specificap-SRS parameters.

FIG. 2 illustrates a multi-carrier 3GPP LTE-A wireless communicationsystem 20 with uplink channel sounding in accordance with one novelaspect. LTE-A system 20 comprises a user equipment UE21 and a basestation eNB22. UE21 comprises memory 31, a processor 32, aninformation-decoding module 33, an SRS and sounding channel allocationmodule 34, and a transceiver 35 coupled to an antenna 36. Similarly,eNB22 comprises memory 41, a processor 42, an information-encodingmodule 43, a channel estimation module 44, and a transceiver 45 coupledto an antenna 46.

For multi-carrier uplink channel sounding, eNB22 configures SRSparameters and allocating SRS resource by transmitting encoded signalinginformation to UE21 in a DL subframe over a primary carrier (e.g.,PCELL). Based on the signaling information, UE21 decodes the SRSparameters and transmits a sounding signal via an allocated soundingchannel in a UL subframe back to eNB22 over an indicated secondarycarrier (e.g., SCELL) for uplink channel estimation. In one or moreexemplary embodiments, the functions described in the uplink soundingprocedure may be implemented in hardware, software, firmware, or anycombination thereof by the different modules. The functions describedabove may be implemented together in the same module, or implementedindependently in separate modules. For example, at the eNB side,information-encoding module 43 prepares an uplink grant with carrierindication information and ap-SRS triggering information, andtransceiver 45 transmits the uplink grant to UE21 over PCELL. At the UEside, information-decoding module 33 detects the carrier indicationinformation and the ap-SRS triggering information, SRS and soundingchannel allocation module 34 maps an ap-SRS in an allocated soundingchannel, and transceiver 35 transmits the ap-SRS back to UE22 over theindicated carrier (e.g., SCELL). Finally, at the eNB side, transceiver45 receives the ap-SRS, and channel estimation module 44 estimatesuplink channel response based on the received ap-SRS.

FIG. 3 is a flow chart of a first method of uplink ap-SRS transmissionin a multi-carrier LTE-A system in accordance with one novel aspect. Themulti-carrier LTE-A system comprises an eNB and a UE. The eNB and the UEare connected over multiple radio frequency carriers including a primaryRF carrier (e.g., PCELL over PCC) and one or more secondary RF carriers(e.g., SCELLs over SCCs). In step 101, the UE receives an uplink ordownlink grant transmitted from the eNB over PCELL. In step 102, the UEdetermines an indicated carrier (e.g., one of the SCELLs) from a carrierinformation field (CIF) in the grant and detects a triggering conditionfor ap-SRS transmission in the grant. If the triggering condition istrue, then the UE select the latest UE-specific RRC messages based onthe value of CIF (step 103). Finally, the UE transmits an ap-SRS overthe indicated carrier using the selected UE-specific SRS parameters(step 104). The first method of uplink ap-SRS triggering mechanism isalso referred to as “UE-specific triggering”.

FIG. 4 illustrates one embodiment of the first “UE-specific triggering”method of uplink ap-SRS transmission mechanism in a multi-carrier LTE-Asystem 40. Multi-carrier LTE-A system 40 comprises an eNB and a UE. TheeNB and the UE are connected over multiple RF carriers including aprimary carrier (e.g., PCELL) and two secondary carriers (e.g., SCELL #0and SCELL #1). The eNB transmits an uplink or downlink grant via aPDCCH. The PDCCH supports various downlink control information (DCI)formats. In each DCI format, there is an information field, which iscalled a “carrier indicator” (CIF). Typically, the “carrier indicator”indicates which carrier should use this uplink grant to do physicaluplink share channel (PUSCH) data transmission or physical downlinkshared channel (PDSCH) data reception. In one novel aspect, ap-SRS istransmitted over the carrier used for PUSCH transmission, which is thecarrier indicated by CIF. In the example of FIG. 4, the value of CIF inthe uplink grant indicates carrier SCELL #1 (e.g., CIF=″#1″). As aresult, PUSCH transmission is scheduled over SCELL #1 based on theuplink grant (e.g., depicted as a grey-shaded area). In addition, ap-SRStransmission is also triggered over the same carrier SCELL #1 based onthe same uplink grant (e.g., depicted as a slash-shaded area).

FIG. 5 illustrates a detailed example of the first “UE-specifictriggering” method of uplink ap-SRS transmission in a multi-carrierLTE-A system 50. Multi-carrier LTE-A system comprises an eNB 51 and aUE52, connected with each other over a primary RF carrier PCELL and asecondary RF carrier SCELL #0. To trigger ap-SRS transmission, eNB 51transmits an uplink grant via a PDCCH 53. In the example of FIG. 5,PDCCH 53 supports DCI Format 4 as illustrated in block 54. DCI format 4contains a “carrier indicator” field (CIF) that is 0 or 3 bits long. TheCIF is “#0” in format 4, and thus indicates the secondary carrier SCELL#0. Upon receiving the uplink grant, UE52 performs PUSCH transmissionover SCELL #0 accordingly. In addition, UE52 also detects any triggeringcondition in the uplink grant and thereby determining whether to triggerap-SRS transmission over SCELL #0. If the triggering condition is true,then UE52 selects the latest UE-specific RRC messages based on the valueof CIF and transmits ap-SRS over SCELL #0 with the selected UE-specificparameters.

In 3GPP LTE-A systems, for configuring p-SRS or ap-SRS parameters, twotypes of SRS parameters are defined in 3GPP LTE-A systems for eachcomponent carrier. A first type of cell-specific parameters includes SRSbandwidth configuration and SRS subframe configuration. Thecell-specific parameters are used to define the overall SRS resourceallocated in a cell served by an eNB. A second type of UE-specificparameters (e.g., illustrated by table 59 in FIG. 5) includes SRSbandwidth allocation, SRS hopping bandwidth, frequency domain position,SRS duration, number of antenna ports, transmission comb, and cyclicshift (CS). The UE-specific parameters are used to define SRS resourceallocation for each individual UE. The cell-specific parameters forp-SRS are re-used for ap-SRS because p-SRS and ap-SRS share the overallSRS resource. The UE-specific parameters for ap-SRS, however, aredifferent from p-SRS such that ap-SRS can use residual resource that isnot used by p-SRS by multiplexing between ap-SRS and p-SRS for each UE.Because cell-specific SRS parameters of p-SRS can be re-used for ap-SRS,only UE-specific parameters need to be selected for ap-SRS transmission.

Because UE-specific SRS parameters are configured via an upper layer RRCsignaling, configuration time is long and signaling flexibility is low.To facilitate efficient SRS configuration, each DCI format is associatedwith one or more pre-defined sets of UE-specific SRS parameters. Asillustrated by table 58 in FIG. 5, DCI Format 0, and Format 3/3A, eachis associated with one set of UE-specific SRS parameters. For example,if DCI format 0 is used in an uplink grant via PDCCH 53, then apredefined SRS parameter set with SRS Bandwidth=BW0, frequency domainposition=k0, transmission comb=comb0, cyclic shift=cs0, and antennaport=p0 is selected. Similarly, if DCI format 1A is used in an downlinkgrant via PDCCH 53, then a predefined SRS parameter set with SRSBandwidth=BW1, frequency domain position=k1, transmission comb=comb1,cyclic shift=cs1, and antenna port=p1 is selected.

On the other hand, DCI format 4 is associated with three sets ofUE-specific SRS parameters. FIG. 5 illustrates an example of DCI format4 with an SRS request having two signaling bits. In the example of FIG.5, eNB51 uses the two signaling bits to configure UE-specific ap-SRSparameters for UE52 via PDDCH 53. The two signaling bits can indicatefour states, including three states for three sets of parametercombinations plus one state for no triggering of ap-SRS. Each of thethree states indicates a predefined parameter combination of SRSbandwidth, frequency domain position, transmission comb, cyclic shift,and antenna port. For example, if SRS request=10, then a predefined SRSparameter set with SRS Bandwidth=BW4, frequency domain position=k4,transmission comb=comb4, cyclic shift=cs4, and antenna port=p4 isselected. UE52 then uses this set of SRS parameters to allocate soundingchannel 56 and generate SRS 57 for ap-SRS transmission over theindicated carrier SCELL #0. The actual values of the pre-defined sets ofUE-specific parameters can be updated or re-configured via RRC signalingwhenever necessary. If SRS request=00, then no ap-SRS transmission istriggered.

FIG. 6 is a flow chart of a second method of uplink ap-SRS transmissionin a multi-carrier LTE-A system in accordance with one novel aspect. Themulti-carrier LTE-A system comprises an eNB and a UE. The eNB and the UEare connected over multiple radio frequency carriers including a primaryRF carrier (e.g., PCELL over PCC) and one or more secondary RF carriers(e.g., SCELLs over SCCs). In step 201, the UE receives a DCI format 3/3Atransmitted from the eNB in PCELL over PCC. In step 202, the UEdetermines triggering information in a plurality of information fieldsin the DCI format. The location of each information field corresponds toan indicated carrier of the UE, while the value of each informationfield corresponds to a triggering condition. If at least one of thetriggering conditions is true, then the UE selects the latest configuredUE-specific SRS parameters (step 203). Finally, the UE transmits anap-SRS over the indicated carrier using the selected UE-specific SRSparameters (step 204). Because a group of UEs may be triggered foruplink ap-SRS transmission via the same DCI format, the second method ofuplink ap-SRS triggering mechanism is also referred to as “group-wisetriggering”.

FIG. 7 illustrates one embodiment of the second “group-wise triggering”method of uplink ap-SRS transmission mechanism in a multi-carrier LTE-Asystem 70. Multi-carrier LTE-A system comprises an eNB71, UE72, andUE73. Base station eNB71 and UE72, UE73 supports four component carriersCC0, CC1, CC2, and CC3. Suppose CC0 is the primary component carrierPCC, and the other three carriers are the SCCs. In a DL subframe, eNB71broadcasts a PDCCH 74 to UE72 and UE73 over the primary carrier CC0.PDCCH 74 has a DCI Format 3/3A. DCI Format 3 is used for thetransmission of the Transmit Power Control (TPC) commands for PhysicalUplink Control Channel (PUCCH) and PUSCH with 2-bit power adjustments.Similarly, DCI Format 3A is used for the transmission of the TransmitPower Control (TPC) commands for PUCCH and PUSCH with 1-bit poweradjustments.

In one novel aspect, a new DCI format similar to DCI format 3/3A is usedto do group triggering of uplink ap-SRS transmission over multiplecarriers. To avoid confusion, the new DCI format is referred to as DCIformat 3′. DCI format 3′ contains K information fields, and each fieldcontains M bits. Additional x padding bits can be added so that thetotal number of bits in format 3′ is equal to that of DCI format 3/3A.DCI Format 3′ is sent to a group of UEs via broadcasting one PDCCH.Different UE groups can be differentiated by different Radio NetworkTemporary Identifier (RNTI) sequence. Within each UE group, each UE canbe assigned N fields among the K information field. For each UE, eachfield indicates if the UE should enable ap-SRS in a specific carrier ornot.

In the example of FIG. 7, block 75 illustrates one example of DCI format3′ in PDCCH 74. In this particular example, the SRS request containstotal 20 information fields, each field contains one bit, and each UE isassigned with four fields (e.g., K=20, M=1, and N=4). UE72 is assignedwith four information fields depicted by slashed shade, and UE73 isassigned with four information fields depicted by grey shade. Withineach UE, each field indicates if the UE should enable ap-SRS in aparticular carrier or not. In other words, the location of each fieldcorresponds to a particular carrier, and the value of each fieldcorresponds to whether ap-SRS is triggered or not. For UE72, fields 2,7, 17, and 20 correspond to CC0, CC1, CC2, and CC3, respectively. Inaddition, because the value of each of those fields equals to 0, 1, 0,and 1, it indicates that ap-SRS is triggered for CC1 and CC3, but notfor CC0 and CC2. Similarly, for UE73, fields 5, 9, 12, and 14 correspondto CC0, CC1, CC2, and CC3, respectively. In addition, because the valueof each of those fields equals to 1, 0, 0, and 1, it indicates thatap-SRS is triggered for CC0 and CC3, but not for CC1 and CC2.

Once the UE determines that ap-SRS is triggered for one or morecarriers, the UE selects SRS parameters and transmits ap-SRS signalsover the indicated carrier(s). For example, UE72 transmits sp-SRSsignals over CC1 and CC3, and UE73 transmits ap-SRS signals over CC0 andCC3 with selected SRS-parameters. For group triggering, cell-specificand UE-specific ap-SRS parameters of each carrier are also configuredfrom RRC. Referring back to FIG. 5, for DCI Format 3/3A, a predefinedSRS parameter set with SRS Bandwidth=BW2, frequency domain position=k2,transmission comb=comb2, cyclic shift=cs2, and antenna port=p2 isselected.

In addition to SRS parameter configuration, the eNB utilizes RRCsignaling to configure each UE the following parameters for grouptriggering: the RNTI sequence which should be monitored for grouptriggering, the index of SRS triggering signal in a group (e.g., thenumber and location of the information fields that belong to each UE),and the corresponding carrier indexes for each UE.

In 3GPP LTE-A systems, both cell-specific SRS parameters and UE-specificSRS parameters need to be configured for p-SRS and ap-SRS. Thecell-specific parameters for p-SRS are re-used for ap-SRS because p-SRSand ap-SRS share the overall SRS resource. The UE-specific parametersfor ap-SRS, however, are different from p-SRS such that ap-SRS can useresidual resource that is not used by p-SRS by multiplexing betweenap-SRS and p-SRS for each UE. Conventionally, there is only one set ofUE-specific SRS parameters for p-SRS, and the parameters are configuredvia RRC signaling when they need to be modified. However, configurationtime via upper layer messaging is long and signaling flexibility is lowif the same signaling method is re-used for ap-SRS. This is especiallytrue for multi-carrier systems, where multiple sets of ap-SRS parametersare supported in each carrier. To facilitate efficient SRSconfiguration, each DCI format is associated with one or morepre-defined sets of UE-specific SRS parameters. Referring back to table58 in FIG. 5, for example, DCI Format 0/3/3A each is associated with oneset of UE-specific SRS parameters, and DCI Format 4 is associated withthree sets of UE-specific SRS parameters. DCI Format 4 supports uplinkMIMO and requires more flexibility of ap-SRS configuration.

In one novel aspect, multi-set RRC signaling is used to configureUE-specific SRS parameters for ap-SRS. Multiple sets of RRC parametersare pre-defined for each UE to signal UE-specific SRS parameters, andeach parameter set contains a subset of the UE-specific parametersincluding: SRS bandwidth allocation, SRS hopping bandwidth, frequencydomain position, SRS duration, number of antenna ports, transmissioncomb, and cyclic shift (CS). Two signaling methods may be used: a jointsignaling method and a separate signaling method. In a joint signalingmethod, multiple sets of UE-specific SRS parameters are signaledtogether in a single RRC message transmission. Joint signaling providessimplicity and flexibility for ap-SRS at the cost of RRC signalingoverhead. In a separate signaling method, each set of UE-specific SRSparameters is signaled independently. If one set of parameters needs tobe re-configured, then that set of parameters is signaled via RRCwithout the need to signal other sets of parameters. This providesenhanced signaling flexibility with reduced signaling overhead,especially if the number of sets is large. However, if thereconfiguration does not happen frequently, joint signaling is better.Moreover, A new information element (IE) (e.g., setNumber), is requiredto indicate which set is re-configured, for separate signaling method.

FIG. 8 illustrates a method of joint signaling of multiple sets ofUE-specific SRS parameters via RRC in a multi-carrier LTE-A system 80.Multi-carrier LTE-A system comprises an eNB81 and a UE82, connected witheach other over a primary RF carrier PCELL and a secondary RF carrierSCELL #0. To configure UE-specific SRS parameters, eNB81 transmits allsets of ap-SRS parameters together via a single RRC message 83. Asillustrated in FIG. 8, the SRS parameters are configured (e.g., byap-SRS configuration module 87) as part of physical parameters (i.e.,AperiodicSoundingRS-UL-ConfigDedicated) of the RRC messageRRCConnectionReconfiguration. The secondary cell (Scell) index is givenin sCellToAddModList-r10. A single RRC message can configure or modifyap-SRS parameters for multiple Scells simultaneously. Two RRC formatsmay be used for the joint signaling. The content of RRC message can beencoded by direct signaling or delta signaling method. For directsignaling method, each parameter of each set is signaled directlywithout any further processing. For delta signaling method, someparameters are signaled in a “differential” way. For example, areference point is chosen, and the differential value between thereference point and each parameter is signaled to save signalingoverhead. In one novel aspect, the Pcell is the reference point.

In the example of FIG. 8, direct signaling method is used, where eachparameter of each set of UE-specific parameters is signaled directlywithout any further processing. For example, the physical parameters ofAperiodicSoundingRS-UL-ConfigDedicated include a sequence ofaperiodicConfigSet. The maximum number of RRC parameter sets ismaxAperiodicConfigNum, and each aperiodicConfigSet contains the valuesof a subset of UE-specific parameters including SRS bandwidth, frequencydomain position, transmission comb, cyclic shift, and number of antennaport. The exact value of each parameter for each set is directlysignaled via RRC message 83.

To trigger ap-SRS transmission, eNB81 transmits an uplink grant via aPDCCH 84. For example, PDCCH 84 supports DCI Format 4 and contains a“carrier indicator” field (CIF) “#0” indicating the secondary carrierSCELL #0. Upon receiving the uplink grant, UE82 performs PUSCHtransmission 85 over SCELL #0 accordingly. In addition, UE82 alsodetects any triggering condition in the uplink grant and therebydetermining whether to trigger ap-SRS transmission over SCELL #0. If thetriggering condition is true, then UE82 selects the latest UE-specificSRS parameters configured by RRC message 83 based on the value of CIFand transmits ap-SRS 86 over SCELL #0 with the selected UE-specificparameters.

FIG. 9 is a flow chart of a method of multi-set RRC signaling for ap-SRSconfiguration from eNB perspective. In step 901, an eNB transmits aplurality of sets of UE-specific SRS parameters to a UE via upper layermessaging in a multi-carrier wireless communication system. In step 902,the eNB determines triggering information of a selected set ofUE-specific SRS parameters and an indicated carrier for the UE. In step903, the eNB transmits an uplink or downlink grant over a primarycarrier, the grant comprises triggering information for the UE to sendan ap-SRS over the indicated carrier using the selected set ofUE-specific SRS parameters. In one embodiment of joint signaling, theplurality of sets of UE-specific SRS parameters are signaled together ina single RRC transmission. In another embodiment of separate signaling,each set of UE-specific SRS parameters is signaled independently.

FIG. 10 is a flow chart of a method of multi-set RRC signaling forap-SRS configuration from UE perspective. In step 1001, a UE receives aplurality of sets of UE-specific SRS parameters from a base station viaupper layer messaging in a multi-carrier wireless communication system.In step 1002, the UE receives an uplink or downlink grant from the basestation over a primary carrier, the grant comprises triggeringinformation for the UE to send an ap-SRS over an indicated carrier usinga selected set of UE-specific SRS parameters. In step 1003, the UEtransmits the ap-SRS over the indicated carrier using the selected setof UE-specific SRS parameters. In one embodiment of joint signaling, theplurality of sets of UE-specific SRS parameters are signaled together ina single RRC transmission. In another embodiment of separate signaling,each set of UE-specific SRS parameters is signaled independently.

In one novel aspect, the multi-carrier system can be deployed as a LTE-Asystem in conjunction with other wireless communication system, such asWiFi or cognitive radio (CR). In such deployment, Pcell is referred to acarrier in the LTE-A system and Scells are referred to the othercommunication system.

Although the present invention has been described in connection withcertain specific embodiments for instructional purposes, the presentinvention is not limited thereto. Accordingly, various modifications,adaptations, and combinations of various features of the describedembodiments can be practiced without departing from the scope of theinvention as set forth in the claims.

What is claimed is:
 1. A method comprising: transmitting a plurality ofsets of UE-specific sounding reference signal (SRS) parametersassociated with aperiodic SRS (ap-SRS) transmission over differentcarriers to a user equipment via upper layer messaging in amulti-carrier wireless communication system, wherein the plurality ofsets of UE-specific SRS parameters are jointly signaled together via asingle radio resource control (RRC) message; determining a selected setof UE-specific SRS parameters and an indicated carrier for the UE; andtransmitting a grant to the UE over a primary carrier, wherein the grantcomprises information for the UE to send an aperiodic SRS (ap-SRS) overthe indicated carrier using the selected set of UE-specific SRSparameters, and wherein the grant further comprises a carrier indicatorfield indicating the indicated carrier.
 2. The method of claim 1,wherein each set of UE-specific SRS parameters comprises an SRSbandwidth, a frequency domain position, a transmission comb, a cyclicshift, and a number of antenna ports.
 3. The method of claim 1, whereinthe plurality of sets of UE-specific SRS parameters are configured aspart of physical parameters of the RRC message, and wherein the RRCmessage configures ap-SRS for multiple secondary carriers.
 4. The methodof claim 1, wherein the grant is transmitted in a physical downlinkcontrol channel (PDCCH) that supports multiple downlink controlinformation (DCI) formats, and wherein each DCI format corresponds toone or more sets of predefined UE-specific SRS parameters configured viaupper layer messaging.
 5. The method of claim 1, wherein the SRSparameters are transmitted via direct signaling or delta signaling.
 6. Abase station, comprising: an information encoding module that encodes aplurality of sets of UE-specific SRS parameters associated withaperiodic SRS (ap-SRS) transmission over different carriers for a userequipment (UE); and a transmitter that transmits the plurality of setsof UE-specific SRS parameters via upper layer messaging over a primarycarrier, wherein the plurality of sets of UE-specific SRS parameters arejointly signaled together via a single radio resource control (RRC)message, wherein the transmitter also transmits a grant to the UE overthe primary carrier, and wherein the grant comprises triggeringinformation for the UE to send an aperiodic SRS (ap-SRS) over anindicated carrier using a selected set of UE-specific SRS parameters,and wherein the grant further comprises a carrier indicator fieldindicating the indicated carrier.
 7. The base station of claim 6,wherein each set of UE-specific SRS parameters comprises an SRSbandwidth, a frequency domain position, a transmission comb, a cyclicshift, and a number of antenna ports.
 8. The base station of claim 6,wherein the plurality of sets of UE-specific SRS parameters areconfigured as part of physical parameters of the RRC message, andwherein the RRC message configures ap-SRS for multiple secondarycarriers.
 9. The base station of claim 6, wherein the grant istransmitted in a physical downlink control channel (PDCCH) that supportsmultiple downlink control information (DCI) formats, and wherein eachDCI format corresponds to one or more sets of predefined UE-specific SRSparameters configured via upper layer messaging.
 10. The base station ofclaim 6, wherein the SRS parameters are transmitted via direct signalingor delta signaling.
 11. A method comprising: receiving, by a userequipment, a plurality of sets of UE-specific sounding reference signal(SRS) parameters from a base station via upper layer messaging in amulti-carrier wireless communication system, wherein the plurality setsof UE-specific SRS parameters are associated with aperiodic SRS (ap-SRS)transmission over different carriers by the UE, and wherein theplurality of sets of UE-specific SRS parameters are jointly signaledtogether via a single radio resource control (RRC) message; receiving agrant from the base station over a primary carrier, wherein the grantcomprises triggering information for the UE to send an aperiodic SRS(ap-SRS) over an indicated carrier using a selected set of UE-specificSRS parameters, and wherein the grant further comprises a carrierindicator field indicating the indicated carrier; and transmitting theap-SRS over the indicated carrier using the selected set of UE-specificSRS parameters.
 12. The method of claim 11, wherein each set ofUE-specific SRS parameters comprises an SRS bandwidth, a frequencydomain position, a transmission comb, a cyclic shift, and a number ofantenna ports.
 13. The method of claim 11, wherein the plurality of setsof UE-specific SRS parameters are configured as part of physicalparameters of the RRC message, and wherein the RRC message configuresap-SRS for multiple secondary carriers.
 14. The method of claim 11,wherein the grant is transmitted in a physical downlink control channel(PDCCH) that supports multiple downlink control information (DCI)formats, and wherein each DCI format corresponds to one or more sets ofpredefined UE-specific SRS parameters configured via upper layermessaging.
 15. The method of claim 11, wherein the SRS parameters aretransmitted via direct signaling or delta signaling.
 16. The method ofclaim 11, wherein each SRS parameter is signaled directly withoutfurther processing.
 17. The method of claim 11, wherein a part of theSRS parameters are signaled in a differential way as compared to areference point.
 18. A user equipment (UE) comprising: a receiver thatreceives a plurality of sets of UE-specific sounding reference signal(SRS) parameters from a base station via upper layer messaging in amulti-carrier wireless communication system, wherein the plurality setsof UE-specific SRS parameters are associated with aperiodic SRS (ap-SRS)transmission over different carriers by the UE, wherein the plurality ofsets of UE-specific SRS parameters are jointly signaled together via asingle radio resource control (RRC) message, wherein the UE alsoreceives a grant from the base station over a primary carrier, whereinthe grant comprises triggering information for the UE to send anaperiodic SRS (ap-SRS) over an indicated carrier using a selected set ofUE-specific SRS parameters, and wherein the grant further comprises acarrier indicator field indicating the indicated carrier; and atransmitter that transmits the ap-SRS over the indicated carrier usingthe selected set of UE-specific SRS parameters.
 19. The UE of claim 18,wherein each set of UE-specific SRS parameters comprises an SRSbandwidth, a frequency domain position, a transmission comb, a cyclicshift, and a number of antenna ports.
 20. The UE of claim 18, whereinthe plurality of sets of UE-specific SRS parameters are configured aspart of physical parameters of the RRC message, and wherein the RRCmessage configures ap-SRS for multiple secondary carriers.
 21. The UE ofclaim 18, wherein the grant is transmitted in a physical downlinkcontrol channel (PDCCH) that supports multiple downlink controlinformation (DCI) formats, and wherein each DCI format corresponds toone or more sets of predefined UE-specific SRS parameters configured viaupper layer messaging.
 22. The UE of claim 18, wherein the SRSparameters are transmitted via direct signaling or delta signaling. 23.The UE of claim 18, wherein each SRS parameter is signaled directlywithout further processing.
 24. The UE of claim 18, wherein a part ofthe SRS parameters are signaled in a differential way as compared to areference point.